In a Small Computer System Interface (SCSI) bus-based system, each SCSI peripheral device is addressable for communication purposes by way of an assigned SCSI bus address or ID. Typically in the prior art, this bus address is hardwired in the device or device back plane connector. While this address designation may be altered, as is desirable during system configuration, such alteration is inconvenient since it requires manual intervention with the system.
One known and widely-used technique for assigning physical addresses to devices on the SCSI bus involves the removal or installation of jumper or plug connections on the device connector of the SCSI bus back plane. Device installation is thus difficult because the user must access and modify individual device connections at the back plane through a panel at the rear of the system enclosure. Another prior art technique, such as the switchable bus termination and address selector described in U.S. Pat. No. 4,920,339, assigns the address for each device by setting a switch (e.g., dual inline packaged "DIP" or rotary type) mounted on the exterior of the device housing to the desired address. This approach eliminates the user's need for directly accessing the back plane, but has certain drawbacks associated with it. It shares in common with the first approach the disadvantage of requiring that each individual SCSI bus address be set manually. Moreover, each SCSI compatible device must be designed to include a selector apparatus. Lastly, such an approach does not allow a user to take full advantage of the wide (16-bit) SCSI bus ANSI standard by utilizing existing 8-slot (device) SCSI enclosures or shelves in support of up to 16 devices.
U.S. Pat. No. 5,175,822 describes a master interface reconfiguration routine executed by a master device on the SCSI bus to dynamically assign addresses to peripheral devices in an existing bus structure. Address configuration information is transmitted by the master device over the SCSI bus to a peripheral device, which then propagates subsequent configuration information to an adjacent device. Such an invention is useful in adapting program-controlled address assignment techniques to the SCSI environment, which includes devices with unalterable (i.e., hardwired) addresses. During configuration, the master device maps the addresses of those devices which cannot be reassigned. This solution does not, however, extend the device addressing range of the existing structure.
Therefore, there exists a clearly felt need in the art to provide a system user with the capability of reconfiguring physical device addresses to alter a system configuration and to extend the bus address range as needed without accessing individual devices or back plane connections. Further, it is desirable to enable the user to service up to fifteen devices (host excluded) using only one 8 device slot shelf design.